Signage is often placed at public spaces, in particular locations with high visibility, such as airports, shopping malls, train stations or sport arenas. Signs include static boards, such as wooden boards, provided with a fixed image by means of printing or painting or the like. Recent developments in display technology have led to the introduction of active boards that are provided with a display device, such as LED boards. In one typical application, active or static boards can extend along the side of a sports field, to display advertisements or other announcements. The messages displayed by an active screen may be captured by a TV camera and broadcast or recorded with the actual sports event, so that a large audience may be achieved for the messages. At the same time, the signs and the images being displayed thereon may be viewed by the spectators that are present at the location of the event itself.
In relation to static boards, WO 01/58147 A1 discloses a method for modifying a visible object shot with a television camera. The object is marked by means of one or more marking surfaces disposed in the area of the object or in its vicinity. WO 01/58147 A1 discloses a rectangular advertisement in which all corners are marked with reference objects, e. g. circles of a given color, by means of which the location of the object in the television picture can be accurately defined. The marking surfaces are identifiable on the basis of radiation differing from other radiation in the area being shot, at least one of said marking surfaces differing in radiation from the environment on the basis of a property other than the color of visible light. The marking surface is identified using at least one identifying detector which is separate from the detectors of the television camera and by means of which the object is shot substantially from the same shooting direction with the television camera. The relationship between the picture coordinates of the television camera and those of the identifying detector is determined, the areas of the object that are visible in the television picture are determined by means of marking surfaces detected, the video signal of the television picture for the areas corresponding to the object is modified in a predetermined manner, and the modified video signal is transmitted.